[hibernate-issues] [Hibernate-JIRA] Commented: (EJB-375) getSingleResult potentially generates out of memory by calling list()

[Pascal P. Pochet (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/EJB-375?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_30882 ] 

Pascal P. Pochet commented on EJB-375:
--------------------------------------

you have setMaxResults() that calls selection.setMaxRows() and selection has getMaxRows() which is not reflected by the wrapping query,
and by adding a local variable int maxResults you store an information already available somewhere else...

so at first it's just "aesthetical" (symetry, avoid copy of info, ...)...

note that with your patch [as I understand (am I wrong ?)]

if maxResults is -1 at entry the underlaying selection maxRows will be left to 2...
when it should be reset to null... because the API goes from int to Integer when crossing query/selection border 
other changes may be necessary... (there is no clearMaxRows()/clearMaxResults() functionality in the API...)

(also a comment about the state of maxResults and the underlaying maxRows in case of exception would be nice...)






> getSingleResult potentially generates out of memory by calling list()
> ---------------------------------------------------------------------
>
>                 Key: EJB-375
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/EJB-375
>             Project: Hibernate Entity Manager
>          Issue Type: Bug
>          Components: EntityManager
>    Affects Versions: 3.3.2.GA
>         Environment: any
>            Reporter: Pascal P. Pochet
>            Assignee: Emmanuel Bernard
>             Fix For: 3.4
>
>
> calling list() while the user expects a single result has potential major flow: it's easy to trigger an out of memory situation where nobody would expect it...
> like getSingleResult("select CURRENT_TIME from AN_ENTITY_CONTAINING_ZILLIONS_OF_RECORDS") ;
> (and it is also a performance problem when it doesn't trigger the out of heap space... and a design issue: why fetching something the caller is not asking for ? with all the consequences on the cache...)
> easy to circumvent by changing
> 			List result = query.list();
> to
> 			List result = query.setMaxResults(2).list();
> (so we keep the functionality of alerting developer when query is wrongly returning multiple results when it should not...)
> and
> 					em.throwPersistenceException( new NonUniqueResultException( "result returns " + uniqueResult.size() + " elements") );
> to
> 					em.throwPersistenceException( new NonUniqueResultException( "result returns more than 1 element") );

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